The present invention relates generally to pneumatic tires, and more particularly to a raw pneumatic tire carcass and a method of fabricting same.
One problem confronting tire manufacturers in the course of fabricating raw tire carcasses, of either the "radial" ply variety or the "bias" ply variety, relates to a weakening or deterioration of the raw carcass when it is inflated from a cylinder to a torus and vulcanized in a toroidal mold. This problem is due to air-entrapment between the interior of the carcass and the outer surface of the bladder in the mold for inflating the carcass into a torus.
A second problem involves the reduction in thickness that the air-impervious carcass liner undergoes in the vicinity of the median equatorial plane thereof when the carcass (of the so-called "tubeless" tire variety) is inflated from a cylinder to a torus, and the resultant loss in the capacity of the liner to effectively resist the permeation or flow of air therethrough.
The problem of air-entrapment is the concern of U.S. Pat. No. 3,143,155 issued on Aug. 4, 1964 to H. W. Knox, in which there is disclosed means for evacuating air or other fluids tending to collect between the carcass-inflating bladder and the interior of the carcass in a mold. This is accomplished by the provision of grooves or small passageways extending along the internal surface of the carcass and acting to direct the outflow or egress of fluid or air confined between the bladder and interior of the carcass. Complete air evacuation, however, is not necessarily insured simply by the principles established in the aforementioned patent.
The problem relating to the reduction in thickness that the air-impervious liner undergoes when inflated into a torus is generally overcome by fabricating the liner with an increased thickness to allow for the thinning thereof when inflated. The thicker liner better resists the permeation of air therethrough, but is more costly and bulky than necessary.